On 24 November 2015 at 15:27, Ned Batchelder <n...@nedbatchelder.com> wrote: > On Tuesday, November 24, 2015 at 10:10:51 AM UTC-5, Antoon Pardon wrote: >> Op 24-11-15 om 15:18 schreef Ned Batchelder: >> >> > 2) In Python, "value" means, what object does a name refer to, or what >> > object did an evaluation produce. >> >> I don't think this is correct because that would imply that objects don't >> change values (since the value would be the object). > > Sorry, I should have been more precise. Python documentation suffers from > this two-meaning world also. There are places where "value" is used in > this second sense, perhaps more places than you realize. I know when I > wrote "Python Names and Values", I meant it in this second sense.
Hi Ned, I read your talk on this subject which was linked to further up in the thread and it is excellent so thanks for that. I forwarded it to a colleague for inspiration in our own introductory programming (with Python) teaching unit. However when I read it and imagined explaining it to our students I found myself wanting to adjust the terminology. I would not use the word value in the way that you suggest. Rather I would want to contrast "names" (or "references"), "objects" and "values". I think that many things can be expressed more cleanly with these terms and I think it corresponds more to the way in which I see Python programmers use these terms. So I would say that an object has a value. Immutable objects have unchanging values but the value of mutable objects can change. The expression "a is b" determines whether or not a and b are bound to the same object whereas "a == b" determines if the objects bound to a and b have the same value. To copy an object is to create a new object having the same value as the copied object. To mutate an object is to change its value etc. Earlier in this thread you said: """ In Python, a default value expression for a function argument is evaluated only once, when the function is defined. That value (in this case, the actual list) is stored with the function. The expression is not stored, the value of the expression is. That value (the actual list) is supplied as the value of the argument if no other value is supplied. If you modify that value in the function, the value is modified, and used again at the next function call. """ I think that's a good example of where it would be clearer to distinguish between objects and values, rather than using the word value for both. In particular what is stored with the function is the *object* that results from the default value expression. The *value* of that object may change if it is mutated but it will still be the same object each time the function is called (without a corresponding argument being passed). -- Oscar -- https://mail.python.org/mailman/listinfo/python-list
